This invention relates generally to flexible rolls and particularly rolls for applying pressure to a substrate passing beneath and in contact with such
There are a number of different applications in which flexible rolls or other mechanical devices are utilized in processing equipment to press downwardly onto the upper surface of a material being processed for the purpose of applying weight or pressure to such material. For example, in equipment used to make corrugated cardboard, the skins and the intermediate web of the cardboard are brought together and moved across the heated surfaces of a plurality of steam boxes so that the heat will cause an applied adhesive to become tacky, while pressure is applied simultaneously to the top surface of the top skin components together with sufficient force to cause bonding thereof. It is common practice to use relatively heavy steel rolls for this purpose, and the rolls are mounted for free vertical movement above the substrate so the weight of the roll itself provides the bonding pressure to the substrate, and the roll rotate freely as the roll engages the substrate.
However, in many such applications of pressure-applying rolls, the width of the substrate is quite large (e.g., 87 inches in the case of a typical cardboard making machine of the type described above and, therefore, the span of the pressure rolls extending across this width must also be quite large. Moreover, the roll must extend across the entire width of the substrate and, therefore, the roll can only be supported at its ends. As a result, when the surface that supports the moving substrate (e.g., the upper surface of the steam boxes) assumes a bowed configuration because of the substantial span thereof, a straight, solid steel roll tends to have less of a bow across its span and the roll applies too much pressure to the substrate at the outer widthwise ends thereof and too little pressure along the rest of the width. In some applications, this can result in a substantial and undesirable gap between the heated surface of the steam box and the surface of the substrate that can affect the operation and/or efficiency of the equipment. For example, a gap of only 1/8 inch between the lower skin and the surface of the steam box over which it travels can result in a loss of about half of the heat generated by the steam box.
In an effort to overcome this problem, pressure rolls of the aforementioned type have been covered with some form of resilient material (e.g., rubber) to add resiliency to the surface of the roll, and while this may improve to some extent the uniformity at which the pressure is applied to the substrate, there is still a significant difference between the pressure applied at the ends of the roll and the pressure applied at the center.
Also, in some cardboard making equipment, rolls have been replaced with a plurality of pressure applying units that are mounted on individual support bars and arranged in side-by-side relation along a portion of the traveling length of the substrate. Each such unit includes a pair of flat plates mounted in spaced parallel relation to one another by a plurality of flexible arms that permit some relative vertical movement of the lower plate or shoe, which is in contact with the upper moving surface of the substrate. Again, this arrangement improves to some extent the uniformity at which pressure is applied to the substrate, but these units are relatively expensive and because the surfaces of each shoe is flat, it is still not possible for such surface to conform closely to the inherent bowing and undulations of the upper surface of the moving substrate.
Finally, it is generally known that rolls can be formed of helically wound metal to provide the roll with particular features suitable for special applications. In many such rolls, the wound outer surface is supported directly on a core so as to have little longitudinal flexibility, as disclosed for example in U.S. Pat. Nos. 798,072; 3,604,087; 3,791,731; and 4,149,303. In other known rolls of this type, the length of the roll is relatively short, at least relative to the resiliency of the wound outer portion of the roll and, therefore, the wound outer portion maintains essentially a cylindrical configuration along its entire length, as disclosed for example in U.S. Pat. Nos. 331,328; 727,838; and 1,271,194.
The present invention provides a roll which overcomes to a substantial extent the aforesaid drawbacks of known arrangements for applying pressure to a substrate and offers a simple, relatively inexpensive and effective pressure applying roll.